Chemical Composition Dependent Elastic Strain in AlGaN Epilayers

Systematic investigations are performed on a set of Al_xGa1−xN/GaN heterostructures grown by metalorganic chemical vapor deposition on sapphire (0001). The Al composition x is determined by Rutherford backscattering. By using high resolution x-ray diffraction and the channeling scan around an off-normal <1213> axis in 1010 plane of the AlGaN layer, the tetragonal distortion e_T caused by the elastic strain in the epilayer is determined. The results show that e_T in the high-quality AlGaN layers is dramatically influenced by the Al content.